The present invention relates to a photocathode and to a method of manufacturing a photocathode.
A photocathode having an optical response in the infrared range and which is made of silver, oxygen and cesium (Ag-O-Cs) is well known in the art. Such a photocathode is described in Sommer, A.: "Photo-emissive Materials" (John Wiley and Sons Inc., 1968). As discussed at pages 134 to 140 of this publication, the most suitable thickness of the silver film layer is in a range of 100 to 200 .ANG.. A photocathode formed accordingly has an optical response in the infrared range up to a wavelength of 1.2 microns.
The present inventor has proposed a photocathode which is made of silver, silver oxide, potassium and cesium and which is sensitive at longer wavelengths than that in which the aforementioned silver-oxygen cesium photocathode is sensitive, and also disclosed a method of manufacturing such a photocathode (see Japanese Patent Application Publication No. 11181/1984). In the wavelength range in which the silver oxygen-cesium photocathode is sensitive, the photocathode previously proposed by the present inventor is more sensitive and has an optical response in the wavelength range of up to 1.7 microns. Thus, the photocathode previously proposed by the inventor is considerably sensitive in the infrared range; however, it is still disadvantageous in that, when it is used in a spectrum analyzer or the like, the gain is variable.